If making the sweet potato puree and pie crust from scratch, prepare them at the same time. Place the potatoes in the oven right before you start making the pie crust.
Preheat the oven to 350°F (180°C).
Have 1 9-inch pie crust, pre-baked.
In a large bowl, mix 2 cups warm mashed sweet potatoes with ⅓ cup unsalted butter, softened, until the butter is fully melted.
Add ⅔ cup granulated sugar and ⅛ teaspoon baking powder and stir to mix well.
Add 2 eggs, 1 teaspoon vanilla extract, 1 teaspoon bourbon, ¼ teaspoon ground cinnamon, a few gratings of fresh nutmeg, ¼ teaspoon lemon zest and ¼ teaspoon orange zest. Mix well without beating; you don't need to incorporate air.
Pour the filling into the prepared crust.
Bake for 40 to 45 minutes, until almost firm in the center. It will be slightly puffed and drier around the edges.
Cool completely on a wire rack. Refrigerate for a few hours so the flavors settle.
Serve cold or at room temperature, plain or topped with whipped cream.
Notes
I use orange sweet potatoes. Three medium ones, about 1 ½ to 2 pounds before baking, make a little more than the 2 cups of mash you need. “Medium” varies, so go by weight. If you’d rather skip the baking, canned puree or homemade puree you already have works the same. Or follow my sweet potato purée post; it shows how to make it. Starting from raw potatoes takes at least 2 to 2 ½ hours: about 1 to 1 ½ hours to bake, 1 hour to drain and 5 minutes to mash.Crust: Both crust posts link in the ingredients show how to blind-bake, so follow those steps before filling the pie.Storage and before serving: Cover the pie and keep it in the fridge for up to a week. I also freeze it and thaw it in the fridge, covered. Take it out about 30 minutes to 1 hour before serving so it’s at room temperature. If the crust has softened in the fridge, warm the pie or a slice in a 300°F (150°C) oven for 10 to 15 minutes on the lower rack, let it cool a few minutes, then add the whipped cream.